Sucker Punch (Combat)

Benefit: If you attack a flat-footed foe in the surprise round of combat with an unarmed attack and successfully strike and damage the target, that foe must make a Fortitude save (DC 10 +1/2 your level or HD + your Strength modifier) or be stunned for 1 round. If the target fails this save by 5 or more, it is instead unconscious for 1d4 rounds (creatures that are immune to critical hits and those that need not sleep are stunned for an additional 1d4 rounds).